CORONAVIRUS

Reports Suggest Many Have Had Coronavirus With No Symptoms

Apr 20, 2020, 6:40 AM | Updated: 6:40 am
FILE (Photo by Brett Carlsen/Getty Images)...
FILE (Photo by Brett Carlsen/Getty Images)
(Photo by Brett Carlsen/Getty Images)

A flood of new research suggests that far more people have had the coronavirus without any symptoms, fueling hope that it will turn out to be much less lethal than originally feared.

While that’s clearly good news, it also means it’s impossible to know who around you may be contagious. That complicates decisions about returning to work, school and normal life.

In the last week, reports of silent infections have come from a homeless shelter in Boston, a U.S. Navy aircraft carrier, pregnant women at a New York hospital, several European countries and California.

The head of the U.S. Centers for Disease Control and Prevention says 25% of infected people might not have symptoms. The vice chairman of the Joint Chiefs of Staff, Gen. John Hyten, thinks it may be as high as 60% to 70% among military personnel.

None of these numbers can be fully trusted because they’re based on flawed and inadequate testing, said Dr. Michael Mina of Harvard’s School of Public Health.

Collectively, though, they suggest “we have just been off the mark by huge, huge numbers” for estimating total infections, he said.

Worldwide, more than 2.3 million infections and more than 160,000 deaths have been confirmed. The virus has caused nearly unprecedented economic and social harm since its existence was reported in early January.

STEALTH CASES

Based on known cases, health officials have said the virus usually causes mild or moderate flu-like illness. Now evidence is growing that a substantial number of people may have no symptoms at all.

Scientists in Iceland screened 6% of its population to see how many had previously undetected infections and found that about 0.7% tested positive. So did 13% of a group at higher risk because of recent travel or exposure to someone sick.

Aboard the aircraft carrier USS Theodore Roosevelt, where one crew member died from the virus, “the rough numbers are that 40 percent are symptomatic,” said Vice Adm. Phillip Sawyer, deputy commander of naval operations. The ratio may change if more develop symptoms later, he warned.

In New York, a hospital tested all pregnant women coming in to deliver over a two-week period. Nearly 14% of those who arrived with no symptoms of coronavirus turned out to have it. Of the 33 positive cases, 29 had no symptoms when tested, although some developed them later.

Previously, tests on passengers and crew from the Diamond Princess cruise ship found nearly half who tested positive had no symptoms at the time. Researchers estimate that 18% of infected people never developed any.

FLAWED METHODS

These studies used tests that look for bits of the virus from throat and nose swabs, which can miss cases. Someone can test negative one day if there’s not much virus to detect and then positive the next.

Symptoms also may not appear when someone is tested but turn up later. One Japanese study found more than half of those who had no symptoms when they tested positive later felt sick.

Better answers may come from newer tests that check blood for antibodies, substances the immune system makes to fight the virus. But the accuracy of these, too, is still to be determined.

On Friday, researchers reported results from antibody tests on 3,300 people in California’s Santa Clara county: Between 1.5% and 2.8% have been infected, they claimed. That would mean 48,000 to 81,000 cases in the county — more than 50 times the number that have been confirmed.

The work has not been formally published or reviewed, but some scientists were quick to question it. Participants were recruited through Facebook ads, which would attract many people likely to be positive who have had symptoms and want to know if the coronavirus was the reason. Some neighborhoods also had way more participants than others, and “hot spots” within the county might have made infections seem more common than they are elsewhere.

Ships, maternity wards and single counties also don’t provide data that can be used to generalize about what’s happening elsewhere. And many of the figures have come from snapshots, not research on wide populations over time.

NEXT STEPS

Antibody testing in particular needs to be done “in an unbiased approach” on groups of people that are representative of the geographic, social, racial and other conditions, Mina said.

The CDC and other groups plan such studies, and they could guide public health advice on returning to normal life for people in certain areas.

If infections are more widespread than previously understood, it’s possible that more people have developed some level of immunity to the virus. That could stifle the spread through what’s called herd immunity, but scientists caution that there is still much to learn about whether mild illnesses confer immunity and how long it might last.

It will probably be months before enough reliable testing has been done to answer those questions and others, including how widespread infections have been and the virus’s true mortality rate, which has only been estimated so far.

“If they’ve all seen the virus before, then maybe you can relax in that neighborhood” and ease social distancing, Mina said. “We’re not anywhere close where we need to be” on antibody testing to do that yet, he said.

___

AP writers Mike Stobbe in New York and Robert Burns and Lolita Baldor in Washington contributed to this report.

___

The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.

KSL 5 TV Live

Top Stories

Coronavirus

CHICAGO, ILLINOIS - SEPTEMBER 09: A pharmacist prepares to administer  COVID-19 vaccine booster sho...
Jed Boal

University Health recommends getting omicron booster and flu shot now

The CDC approved the COVID-19 bivalent boosters that target the most recent omicron variants on September 1. Since then, tens of thousands of Utahns have rolled up their sleeves.
2 days ago
FILE: Pfizer-BioNTech COVID-19 (left) and Moderna COVID-19 (right) vaccines are seen at a vaccinati...
Jed Boal

Despite reaching 5,000 deaths, Utah’s COVID-19 numbers are down

The director of the World Health Organization said yesterday about COVID-19, “the end is in sight,” even if we are not there yet.
13 days ago
FILE PHOTO (Photo by Al Bello/Getty Images)...
Associated Press

WHO: COVID end ‘in sight,’ deaths at lowest since March 2020

The head of the World Health Organization says the number of coronavirus deaths last week was the lowest reported number in the pandemic since March 2020, marking what could be a turning point in the years-long global outbreak.
13 days ago
A school classroom with chairs and desks...
Brooke Williams

Project to provide air purifiers in Utah K-12 classrooms

Cleaner air improves student performance, decreases COVID transmission and school absenteeism. New project provides air purifiers for classrooms in Utah.
14 days ago
SHANGHAI, CHINA - JULY 08: People walk by a closed store at a neighborhood designated as a medium-r...
Laura He, CNN Business

Zero- COVID-19 at what price? Chinese researchers are treading on sensitive ground

Authorities in Shanghai have denied a report by a leading Chinese real estate research firm that claimed more than a third of shops in a major mall had been shuttered because of strict COVID-19 curbs.
16 days ago
FILE: Pfizer-BioNTech COVID-19 (left) and Moderna COVID-19 (right) vaccines are seen at a vaccinati...
LAURA UNGAR AP Science Writer

Is COVID-19 winding down? Scientists say no

New booster shots have arrived and social distancing guidelines have eased but COVID-19 infections aren't going away anytime soon. Experts predict the scourge that's already lasted longer than the 1918 flu pandemic will linger far into the future as the virus continues to cause deaths and may well mutate or evolve into a new disease.
20 days ago

Sponsored Articles

young woman with stickers on laptop computer...
Les Olson

7 ways print marketing materials can boost your business

Custom print marketing materials are a great way to leave an impression on clients or customers. Read for a few ideas to spread the word about your product or company.
young woman throwing clothes to organize a walk in closet...
Lighting Design

How to organize your walk-in closet | 7 easy tips to streamline your storage today

Read our tips to learn how to organize your walk-in closet for more storage space. These seven easy tips can help you get the most out of your space.
Types of Computer Malware and Examples...
PC Laptops

5 Nasty Types of Computer Malware and Examples | Everything You Need to Know to Keep Your Computer and Family Safe

Here are the different types of computer malware and examples that could potentially infect your computer.
tips how to quit smoking...

7 Tips How to Quit Smoking | Quitting Smoking Might be One of the Hardest Things You Ever Do but Here’s Where You Can Start

Quitting smoking cigarettes can be incredibly difficult. Here are 7 tips how to quit smoking to help you on your quitting journey.
Photo: Storyblocks...
Blue Stakes of Utah 811

Blue Stakes of Utah 811: 5 Reasons To Call 811 Before You Dig When Working in Your Yard

Call before you dig. Even at home, you could end up with serious injuries or broken utilities just because you didn't call Blue Stakes of Utah 811.
Days of...
Days of '47 Rodeo

TRIVIA: How well do you know your rodeo? Take this quiz before you go to the Days of ’47!

The Utah Days of ’47 Rodeo presented by Zions Bank is a one-of-a-kind Gold Medal Rodeo being held July 20-23, 25 at 7:30 PM. The Days of ’47 Rodeo How well do you know your rodeo trivia? Take the quiz to test your know-all before heading out to the Days of ’47 Rodeo at the […]
Reports Suggest Many Have Had Coronavirus With No Symptoms